Propeller ice-prevention heating unit



Jan 5, 1954 G. H. HoLDAwAY ET AL PROPELLER ICE-PREVENTION HEATING UNIT Filed Aug. 5, 1950 .......mmr

YN MN Q GEORGE' H. HOLDWAY ELWY/V 0. WALLACE Qrvm.

MTW., w.

Patented Jan. 5, 1954 OFFICE PROPELLER ICE-PREVENTION HEATING UNIT George H. Holdaway and Elwyn C. Wallace, Mountain View, Calif.

Application August 3, 1950, Serial No. 177,546

2 Claims.

(Granted under Tine a5, U. s. code (1952),

sec. 266) The present invention relates to aircraft propellers and particularly to a deicing device for attachment to propellers.

De-icing devices commonly in use are subject to failure and fouling of the propeilers due to the separation of the external heating element from the surface of the propeller by abrasive action of the air and Water droplets encountered in iiight and stones and other loose abrasive material encountered during engine run-up on the attaching covers or adhesives. Frequent failures have been noted as due to the shorting of the heating element on the metal propeller through wear and rupture of the insulating layer in which the heating element is iixed.

An object of the present invention is to provide a de-icer for an airplane propeller having a more durable thermal and electrical insulating layer to prevent snorting and heat loss through the propeller.

Another object of the invention is to provide such a de-icer for an airplane propeller that is readily applied to variously shaped propeller-s.

A still further object of the invention is to provide a de-icer which is protected against abrasion and one which closely adheres to the aerodynamic shape of the propeller without creating excessive drag.

The embodiment of this invention as well as other objects and advantages thereof will be readily apparent from consideration of the following speciication relating to the annexed drawing in which:

Fig. l is a View in elevation and part section of a propeller blade with the de-icer secured thereon.

Fig. 2 is an enlarged view in section taken on line 2-2 of Fig. 1.

Fig. 3 is an enlarged View in section taken on line 3 3 of Fig. 1.

Fig. 4 is a slightly enlarged view of the outer portions of the heating elements.

Referring to the drawing in which like numerals indicate like parts throughout the several views, the propeller blade I is covered at its leading edge II with a rst layer of a thermally and electrically insulating material suitably secured by cement or other means. Over the layer I2 is cemented a wrapped layer I3 of tape having electrically insulating properties, such as woven glass tape. Woven glass tape conforms readily to the contours of the propeller blade and may be laid without overlapping to completely cover any shape of blade.

Heating elements I4 and I4 are then cemented or otherwise bonded to the layer I3 and positioned along the leading edge I for a distance of approximately ten per cent of the chord length on each side. The heating elements I4, I 4 are thin iiat strips of resistance metal laid parallel approx'imateli7 als of an inch apart, and their ends I5 near the tip of the propeller are joined by short bus bars I6, and I8', each pair of elements I4 forming a heating unit I1, and elements I4', as shown in the arrangement of Fig. 4, are connected in series-parallel to form heating unit I'I' having a greater heat dissipation than units I l. Unit Il is positioned over the leading edge Il where a greater heat is needed. The leads I8, I9, and I8', I9', of the heating units Il, Il', respectively, are connected one to each of the clamping collars 20 and 2| by studs 22. A source of current is connected to the collars 20, 2| in a conventional manner by means not here shown since they are not considered a part of the invention. As is shown in Fig. 4, two of the heating elements I4 in unit Il are connected to one terminal collar 2|, and two to the other terminal collar 20.

A second layer of tape 23 is cemented and Wound over the heating elements I4, I4', over the bus bars I6 and leads I8, I8', I9, and I9 and collars 20, 2l. An abrasion resistant cap strip 24, such as Nichrome metal, is cemented over the leading edge Il in order to protect the heating units l'I, Il'. It has been found that woven glass tape of approximately .005 of an inch in thickness is adequate for layer I3, and one of .003 of an inch in thickness is suitable for layer 23, each of approximately 1/2 inch in Width, and when applied in the manner described provides thermal and electrical insulation for the heating units and prevents undue heat loss through the blade.

Due to the arrangement of the heating elements I 4 in unit I, by connection in seriesparallel, the heat dissipation over the leading edge of the blade will be approximately twice that of the heat dissipation from the areas adjacent.

Experiments have shown that a current dissipation of 9 watts per square inch .for the area on each side of the leading edge and substantially twice that for the area of the leading edge is adequate for most icing conditions. The preferred material for the cap strip is Nichrome metal of .004 of an inch thickness and 2 inches width for the average width propeller blades.

It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention and that numerous modifications or alterations may be made therein Without departing from the spirit and the scope of the invention as set forth in the appended claims.

The invention described herein may be. manufactured and vusedby Vor for @the Qovernmentrof the United States of Americaior :governmental purposes Without the payment of any royalties thereon or therefor.

What is claimed is:

1. In an airplane propeller, "apropeller VVbody having a leading and a trailing edge, a de-icer connected to said body and comprising, a'strip of thermally insulating material extending span- Wise `of the body and disposed on said leading edge, said strip extending `chordvse 'f""said body a distance to substantially cover said leading edge, a layer of insulating .material disposed on and secured to said bodysaid 'layer consist; ing of a strip of insulating material Wound hQrQWie O f Seid badi' ,ald extending completely arhndsad tegenaan@ avantages; a Y @amn-fastened@ ad inerente ienlg Edge OlfSi Q heatingelemriwb.- "irteV iugtapvsedto said .Sti-ip' Of i' lmjg' bliel a'tanee insulating 'mterlal ,@Xtniis arrnliml".Saidv 19 inig :arid 'trailing edges aad' 20"1': ranged to '.fQIm @over "1ere" QYrthefr-Svme:

4 tioned layer and said heating element, and a capstrip at the leading edge of said body disposed over the portions of said layers on said leading edge, said insulating strip and said heat- .ing-element.

v A12"I` l.1ecombinationof'laixn Landgsaid heating element consisting of a plurality of flat bars side-by-side relation, bus bars at the outer dends thereof eonnecting said flat bars, and lead kconductors at Ithe inner ends of said bars, colilars connected to said body at the root thereof,

-andstud s onneetd to one of said collars to mhichgsaid lead conductors are connected.

GEORGE H. HOLDAWAY. ELWYN C. WALLACE.

lReferencuses Cited in the le of this patent vUNITED STATES PATENTS Number `1,86-,168 2120-2320 "2,393,635 2,406,367 2,454,874: 2,487,658 ASQ-2179 @552,915 

